The class of device or function that you want to find.
For a list of class codes, see <hw/pci.h>.
You must OR together a class code and a subclass code (e.g.
PCI_CLASS_DISPLAY | PCI_SUBCLASS_DISPLAY_XGA).

index

The index of the device or function that you want to find: 0 for the
first, 1 for the second, and so on.

bus

The bus number, in the range [0...255].

dev_func

The device or function number of the nth device
or function of the given class.
The device number is in bits 7 through 3, and the function number
in bits 2 through 0.